OBD systems are utilized to continuously monitor vehicle systems and components during vehicle operation for malfunctions and disturbances. Any errors or faults detected by the OBD system are stored in the system's memory, and errors and/or faults can be readily accessed by technicians and operators to facilitate troubleshooting and repairs.
Engine exhaust emissions regulations have become increasingly stringent over recent years. For example, for heavy-duty and medium-duty diesel vehicle applications, the California Air Resource Board (CARB) has mandated OBD monitoring and malfunction detection, with increasingly stringent OBD monitoring requirements scheduled to be phased in over time.
In various jurisdictions, regulations stipulate that all emission-related systems and components must be monitored to detect an increase in toxic exhaust gas emissions in the event of a malfunction. The regulations define malfunction criteria for various exhaust aftertreatment components, such as diesel oxidation catalysts (DOCs), selective catalytic reduction (SCR) catalysts, SCR on filter (SCRF), diesel particulate filters (DPFs), and other components. For example, certain regulations require that a detected malfunction be displayed to the operator via a malfunction indicator lamp (MIL) if a fault results in exhaust emissions exceeding certain thresholds (e.g., 2.0 times the applicable standards). For example, Table 1 below lists malfunction criteria specified by CARB's OBD II regulations for medium-duty diesel vehicles.
TABLE 1California OBD II Malfunction Criteria: Engine certified Medium Duty Diesel VehiclesMonitorModel YearNMHC or CONOxPMNMHC catalyst, NOx conversion2007-20092.5xA.S. + 0.50.09g/bhp-hrbcatalyst, NOx adsorber, PM filter2010-20122.5xA.S. + 0.3-0.40.07g/bhp-hr2013 and later2.0xA.S. + 0.20.03g/bhp-hrcUpstream AFR sensor, VVT, fuelEngines certified to NOx standard >0.50 g/bhp-hrsystem monitor, downstream sensors,2007 and later1.5-2.5x1.5-2.0x0.03-0.05g/bhp-hrcNOx and PM sensors, EGR systemmonitor, boost pressure monitor, coldEngines certified to NOx standard ≦0.50 g/bhp-hrstart emission reduction strategy2007-20122.5xA.S. + 0.3-0.40.03-0.05g/bhp-hrc2013 and later2.0xA.S. + 0.20.03g/bhp-hrcMisfire monitor2010 and later2.0x2.0x0.03g/bhp-hrcA.S.—applicable standard, g/bhp-hrafor 2007 through 2012 model years PM filter malfunction criteria may exclude detection of specific failure modes (e.g., combined failure of partially melted and partially cracked substrates) to prevent significant errors of commissionbfor 2007 through 2009 vehicles certified to a PM emission standard of 0.08 g/bhp-hr or higher, a malfunction criteria of 1.5x the applicable PM standard appliescA malfunction criteria of A.S. + 0.02 may also be used in place of 0.03 g/bhp-hr and A.S. + 0.04 in place of 0.05 g/bhp-hr
Catalysts (e.g., DOCs and SCR catalysts) may deteriorate over time due to several mechanisms. One example catalyst deterioration mechanism is thermal aging, which results from exposure to high exhaust gas temperatures over time. For example, thermal aging can result in sintering of noble metals, loss of oxygen storage capacity, and phase transformation of the washcoat. Thermal aging can reduce a catalyst's conversion efficiency to the point that the catalyst is determined to have malfunctioned. Emissions regulations, such as those listed in Table 1, specify malfunction criteria for detecting malfunctions of various components, such as catalysts.